The thorny dragon or thorny devil (Moloch horridus) is an Australian lizard, also known as the mountain devil, the thorny lizard, or the moloch. This is the sole species of genus Moloch. The thorny devil grows up to 20 cm (8.0 in) in length, and it can live up to 20 years.

Most of these lizards are coloured in camouflaging shades of desert browns and tans. These colours change from pale colours during warm weather and to darker colours during cold weather. These animals are covered entirely with conical spines that are mostly uncalcified.

The thorny dragon also features a spiny "false head" on the back of its neck, and the lizard presents this to potential predators by dipping its real head. The females are larger than the males. The thorny dragon's body is ridged in structure, and this enables the animal to collect water from any part of its body.